Spread spectrum communications involve using more bandwidth than is theoretically needed to transmit digital data. Motivation for using spread spectrum signals is generally based upon interference suppression, energy density reduction or time delay measurement. Direct sequence, pseudonoise, frequency hopping, time hopping and linear frequency modulation are generic types of spread spectrum signals which may be used alone or in combination with each other dependent upon user requirements and system capacity.
In many spread spectrum systems several binary bits are transmitted together in symbols. These symbols may be CCSK, Walsh or others. Often data will be encoded by an error correction code. The correction code has increased accuracy if an estimate of the certainity of bit or symbol decisions are factored into the processing of data. Error correction codes which use this certainty estimate are called soft decision codes.
A matched filter, typically a correlator, provides at its output port the maximum possible peak-signal power/average-noise power ratio when the input is a known signal and a random noise component. Matched filters are implemented in a variety of elements and may be periodic, non-periodic, autocorrelated, or cross-correlated. Implementations may reflect dedicated circuitry for each correlator and associated devices or may be accomplished through adaptive techniques.
Prior art correlators operate by assigning a weighting factor to received signals predetermined and dependent upon, the detected deviation between received packets of coded information often referred to as symbols. This interrelationship between symbols is then used indiscriminately in assigning a soft decision weighting value to all binary bits in a symbol. Unfortunately, weighting all bits in a symbol the same value often results in inaccurate processing of signals due to inappropriate weighting factors being assigned individual bits.
Accordingly a new method of processing coded signals is mandated that allows increased precision of weighting of individual bits and resultant improved accuracy of coded symbol processing.